Doc said it. My 722.6 had it's fluid and filter (and gasket) done at 90,000 kilometers.
The fluid is $20 per here. Not bad considering I only need it done every 4-5 years.
One thing to note is that setting the fluid level requires the tranny dipstick and the tranny temp to be at 80C for it to be correct.
My dealer changed the fluid and filter, set the fluid level properly, and replaced the gasket for about $250 parts and labour. Expensive for a tranny service, but with the long interval it works out to be the same as "conventional" MB trannies.
1998 C230 "Black Betty"